If Rust is generated on a brand-new electric appliance or the rice which is moist when you open a new package, it will be a serious problem that ultimately diminishes the reputation of the manufacturer. Therefore, moisture-proof packaging plays a role in the manufacturer’s quality control. It is widely used in machinery, electronics, foodstuff, medicine and daily care, etc. And it is a most commonly used protection against moisture during logistics. Moisture-proof package avoids rusts and deterioration of the packed contents effectively.
The main effect of moisture-proof packaging is to maintain the water content of the product by employing materials of excellent anti moisture property to limit or avoid moisture from outside entering the package and/or placing desiccants inside to absorb moisture, so that proper shelf life can be prolonged.
Apart from general requirements of pacakaging materials, moisture-proof packaging requires materials of low moisture transmission rate. Commonly used moisture-proof packaging materials include paper, plastic, metal and pottery.
Paper based moisture-proof materials have gained common recognition in recent years, such as moisture-proof cellophane, paraffin paper, polyethylene coated paper, an introduction to the property and applied range are as follows.
Cellophane is a thin, transparent sheet which is made of regenerated collulose, its low permeability to air, oils, greases and bacteria makes it useful for food packaging. Cellulose from wood, cotton, hemp or other sources is dissolved in alkali and carbon disulfide to make a solution called viscose, which is then extruded through a slit into a bath of dilute sulfuric acid and sodium sulfate to reconvert the viscose into cellulose. The film is then passed through several more baths, one to remove sulfur, one to bleach the film, and one to add glycerin to prevent the film from becoming brittle. Chemicals of high resistance to moisture, such as polyethylene, polyvinyl chloride and ethylene vinyl acetate copolymer, are added in papermaking process, which makes it resistant to moisture. It is suitable for food, meat and machinery.
Papaffin paper, or wax paper(waxed paper) is a kind of paper that is mde moisture proof through the application of wax. The practice of oiling parchment or paper, in order to make it semi-translucent or moisture-proof, goes back at least to medieval times. The invention of paraffin paper is often credited to Thomas Edison, although gustave le gray used a type of waxed paper for photographic negative processing. Wax paper is commonly used in cooking, for its non-stick properties, and wrapping food for storage, such as cookies, as it keeps water out or in, it is also used in arts and crafts.
Polythylene coated paper
The reason for coating any paper, with a compound(in this case polyethylene), is to impart some desirable qualities, of the latter, to the former. A pe coated paper is made by a process which is known as extrusion coating. In this process, a coating of plasitc, in its molten state, is extruded onto the paper through a slit dye when the temperature touches 320℃. Following this, it passes through a nip, then holds a rubber-covered pressure roller. Finally, a trip through the chrome-plated cooling roll, cools it back into solid state, and imparts the plastic surface, the desired finish. PE coated paper has thus been an answer to the requirement of these qualities in the packaging industry and addresses the environmental issues, alongside. PE coating not only renders the paper water resistance, but confers it wet strength as well. The latter here refers to the strength with which the fibre-web of paper holds together, against a force of rupture.